The present invention generally relates to bonding methods and apparatus, and more particularly, to an improved heater and bonding method for use in securing an object to a surface.
Prior art relating to the present invention includes mounting ceramic packages such as multichip modules on a circuit module using a thermosetting paste adhesive such as polysulfide. A layer of paste adhesive is applied either to the bottom of the multichip module or directly to the surface of the circuit module. The multichip module is then very carefully positioned, weighted and fixlured onto the adhesive paste such that no sliding movement takes place, and the assembly is placed in an oven to cure the adhesive.
Typical adhesives used for this purpose do not have very high thermal conductivity, which adversely affects the performance of some multichip modules where it is important to remove heat from the module to a heat sink. If the multichip module must be removed from the circuit module for repair, rework, or replacement, it is very difficult to heat the assembly to a high enough temperature to facilitate removal without endangering the components of the multichip module, or the circuit module to which the multichip module is mounted. It is also awkward to fixture the multichip module onto the paste adhesive layer such that it maintains alignment in the required location, and to maintain proper thickness control of the adhesive layer.
The conventional method of bonding multichip modules comprises bonding it with a thermosetting adhesive, typically a polysulfide material, and curing the adhesive in an oven. If the multichip module must be removed for rework or replacement, the entire assembly is heated with hot gas or other suitable means to soften the adhesive and the multichip module is twisted or pried off the module. Polysulfide and other similar adhesives are very tenacious. Often, the package of the multichip module is broken during removal because of high stresses imposed on the package during removal. It is also very difficult and costly to clean the residual thermoset adhesive off the package and the multichip module.
Therefore, it is an objective of the present invention to provide for an adhesive heater and bonding method for use in securing an object to a surface. It is a further objective of the present invention to provide for a adhesive heater and bonding method for use in securing ceramic packages to cimuit modules.